Transport Publication TP 127 E
Electrical Systems Less Than 50 Volts
50. Types of Systems
50.1 Subject to subsection 50.4, all distribution systems shall be of the 2-wire type with insulated feed and return conductors in compliance with subsections 50.2 and 50.3.
50.2 Ungrounded distribution systems shall have all current carrying conductors, including the source of power and all accessories, completely insulated from ground throughout the system.
50.3 Grounded distribution systems shall utilize the common ground part of the vessel only as a means of maintaining the return side of the system at ground potential; the grounded side of the system shall be of negative polarity.
50.4 The engine block may be used as a common ground return for electrical accessories mounted on the engine, except on metallic vessels where the engine block is not electrically isolated from the hull.
51. System Protection
51.1 Electrical systems and equipment shall be protected from the effects of overcurrent by suitably rated fuses or circuit breakers.
51.2 Circuit breakers shall be:
- the proper voltage type and rating;
- be the manual reset type;
- have instantaneous short-circuit protection capable of repeatedly opening the circuit in which they are used without failure; and
- be of trip-free type.
51.3 Fuses of the proper rating may be used for circuit protection, but shall be used in conjunction with a switch located between the fuse and source of power; fuse holders shall be suitable for use in sea atmospheres.
51.4 A master battery isolating switch shall be provided in accordance with the following:
- be capable of carrying the continuous maximum current of the system in each ungrounded conductor;
- the continuous rating of the switch shall be not less than the total ratings of the main overcurrent protection devices connected to it;
- be capable of carrying the intermittent maximum cranking current of the largest engine cranking motor;
- shall be located as close to the battery as practicable but readily accessible in the event of an emergency;
- when used with a diode rectified alternator or third brush generator incorporate a means for breaking the field circuit when the battery load is removed from the system.
51.5 A fuse or manual-reset type circuit breaker shall be provided in each ungrounded feeder to the power distribution panel, except for the battery cable from the battery to the starter.
51.6 A fuse or manual-reset type circuit breaker shall be provided at the main distribution panel for each separate electrical circuit.
51.7 Each ungrounded conductor of circuits supplying lights, motors or electrical accessories shall be protected against overload at the distribution panel or switchboard serving as the source of power; each navigation light branch circuit shall be protected by a separate overcurrent device installed in each ungrounded conductor.
51.8 If, for any reason, the cable size is reduced at a junction box, the rating of the circuit overload protective device shall be based on the current-carrying capacity of the smallest conductor in the circuit.
51.9 The conductors supplying motors and motor-operated appliances shall be protected by an over-current device which is designed to handle the inrush current; the motor protective overload device shall be rated or set at not more than 115 percent of the motor full load current rating for enclosed motors and not more than 125 percent of the rating for open motors.
52. Equipment Grounding
52.1 In steel and aluminum vessels, non-conducting exposed metal parts of electrical equipment that requires to be grounded shall be effectively grounded to the hull.
52.2 On wood and composite ships, a continuous ground conductor shall be installed to facilitate the grounding of non-conducting exposed metal parts of electronic and communication equipment that requires to be grounded; the ground conductor shall terminate at a point on the main engine or at a copper plate of area not less than 0.2 m² fixed to the keel below the light waterline so as to be fully immersed under all conditions of heel.
52.3 Every grounding conductor shall be of copper or other corrosion-resistant material and shall be securely installed and protected, where necessary, against damage and against electrolytic corrosion.
52.4 Every ground connection to the ships structure, or on wood and composite ships, to the continuous ground conductor, shall be made in an accessible position and shall be secured by a screw or connector of brass or other corrosion-resistant material used solely for that purpose.
53. Lightning Conductors
53.1 Lightning conductors shall be fitted to each mast of all wooden and composite vessels and to each mast of steel or aluminum vessels having wooden masts or topmasts except where the height of any antenna exceeds that of the masts and the antenna is equipped with lightning arrestors or other effective devices.
53.2 Lightning conductors shall be composed of continuous copper alloy tape or cable having a cross-sectional area of not less than 25 mm² (# 4 AWG ) which shall be attached by copper rivets or clamps to a copper spike (air terminal ) not less than 13 mm in diameter, projecting at least 150 mm above the top of the mast; the copper alloy tape or cable shall be run to terminate at a copper plate of area not less than 0.2 m² , fixed to the keel below the light water line so as to be fully immersed under all conditions of heel or trim.
53.3 No grounding conductor shall be attached to the lightning conductor plate.
53.4 The copper plate shall be separate from, and in addition the copper plate for terminating the grounding conductor.
54. Electrical Equipment
54.1 Electrical equipment appliances, accessories and fittings shall comply with Part 1 Section 2.7, 2.8 and 2.15.
54.1.1 where special marine-type equipment is required and there is no standard for it, it shall be of type that is safe and effectively fulfils the purpose for which it is intended.
54.2 Electrical equipment shall be of a type suitable for the location and the environment and shall be positioned so as not to be unnecessarily exposed to mechanical damage; light fixtures are to have globes or guards.
54.3 Electrical equipment shall not be installed where explosive or flammable gases or flammable vapours are liable to accumulate or where risk of explosion might arise unless the apparatus is of the certified safe type.
54.4 Electrical distribution panels and electrical equipment shall be located in accessible well-ventilated locations protected from rain and spray; where necessary, drip-proof equipment shall be provided.
55. Batteries
55.1 Batteries shall be located in a compartment, locker or box reserved solely for that purpose; they shall not be located in accommodation spaces; batteries intended for emergency purposes shall be installed in a protected location as high as possible in the vessel.
55.2 Batteries shall not be tapped for voltages other than the total voltage of all the cells comprising the battery.
55.3 Batteries shall be so located that gas generated in charging will be readily dissipated by natural or mechanical ventilation; the ventilation requirements are to comply with Section 19.5 Ventilation of Batteries.
55.4 Batteries shall be accessibly located, provided with suitable supports, and secured against movement arising from the motion of the boat.
55.5 Alkaline and lead-acid batteries shall not be installed in the same compartment.
55.6 Batteries shall be located in a liquidtight tray or liquidtight box of adequate capacity to retain normal spillage or boilover of the electrolyte; the liquidtight tray or box shall be constructed of, or lined with materials resistant to deterioration by the electrolyte.
55.7 A non-conductive, perforated cover or other suitable means shall be provided to prevent accidental shorting of battery terminals.
55.8 Batteries with metal cell containers shall be assembled in non-conductive trays having suitable insulating cell supports; provision shall be made to prevent other conductive materials that could cause a short-circuit from coming in contact with the cell containers.
55.9 Where batteries are used as the primary power source, the battery capacity should be at least 50% greater than the essential load on a 10 hour discharge rate.
55.10 Indication shall be provided that the battery is being maintained in a state of charge.
55.11 Valve regulated or sealed batteries shall meet the installation and location requirements of the applicable subsections of Section 19 ACCUMULATORS and BATTERIES.
56. Cables
56.1 All cables shall have a protective covering of either watertight metallic sheath or impervious non-metallic sheath, compatible with the insulation if an armour is provided it shall be in accordance with Section 12.5.
56.2 Cables may be of a suitable commercial grade with stranded copper conductors and rated for at least 75° C service.
56.3 Portable cords or portable cables shall not be used for fixed wiring.
56.4 Cables shall be effectively supported and secured in order to prevent chafing or other injury; on wood or composite vessels the cables shall be run in metal trays, or shall be secured by clips or straps of non-ferrous material; staples shall not be used for this purpose.
56.5 Cables shall be routed as high as possible above the bilge with prime consideration given to the protection of the wiring from mechanical damage and heat damage.
56.6 Exposed wiring subject to mechanical damage shall be protected by conduit or other equivalent means.
56.7 Cables terminating in equipment capable of generating high temperatures such as lighting fixtures, etc., shall be suitable for operation at the temperature of the equipment.
56.8 Current carrying capacities of cables will be assigned in accordance with Table 12-1, unless otherwise stated by the cable manufacturer.
57. Switchboards & Distribution Panels
57.1 Switchboards and electrical distribution panels shall be located in accessible well ventilated locations protected from rain and spray; where necessary, panels shall be provided with a drip shield.
57.2 Switchboards or other electrical panels or junction boxes located adjacent to weather decks or in open cockpits shall be enclosed or protected from deck wash.
57.3 Switchboards shall be so installed that no pipes or tanks are above them within the same space; where this is unavoidable, pipes shall be without joints in such positions.
57.4 Switchboard bus-bar supports shall be of substantial and durable construction and shall be capable of withstanding electro-mechanical stresses which may arise from short-circuit faults; all panels shall be of substantial construction to withstand vibration, and hinged panels and doors of dead front switchboards shall be provided with positioners and stops.
57.5 Bus-bars and their connections shall be of copper, all connections being made so as to inhibit corrosion.
57.6 Switchboards and panel boards shall be designed so there are no exposed live parts accessible to operating personnel under normal operation.
58. Distribution
58.1 Joints and connections in all electrical conductors shall be mechanically and electrically secure and made only in junction or outlet boxes.
58.2 Joints shall be capable of withstanding the vibration and movement encountered in normal service.
58.3 Metal alloys used shall be corrosion-resistant and galvanically compatible with copper conductors.
58.4 With the exception of the thread cutting type of connector, twist-on type connectors shall not be used for making joints in cables.
58.5 Lampholders shall be constructed wholly of flame-retardant and non-hygroscopic material and supports of live parts should be non-combustible material.
58.6 Lamps which are exposed to the weather, spray and drip shall be enclosed in weatherproof fittings.
58.7 Navigation light installations for systems under 50 volts shall be in accordance with Sections 11.37, 11.38 and 51.7.
58.8 The drop in voltage from the switchboard to every point on the installation when the conductors are carrying the maximum service shall not exceed:
- for lighting circuits, 5% of the nominal voltage; and
- for mains and power circuits, 2% of the nominal voltage.